Enzymes for industrial purposes are usually provided as liquids or amorphous solids. Their availability as amorphous, rather than crystalline, solids is primarily due to the fact that the known methods for crystallization of enzymes are generally regarded as being too expensive to be used on an industrial scale.
There is an abundance of literature concerning crystallization of enzymes. It is difficult to generalize with respect to the outcome of specific crystallization procedures, as the art of enzyme crystallization is highly empirical.
Characteristic requirements of most of the hitherto known protein crystallization processes are: pure, concentrated initial solutions; very long crystallization times; and large amounts of chemicals, e.g. salts [see, e.g., Biotechnology and Bioengineering 48 (1995) pp. 316-323].
An industrial enzyme crystallization process which employs a water-soluble polymer (such as polyethylene glycol) has been described (see WO 95/01989).